A slightly different Z Head question....maybe

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Model T Ford Forum: Forum 2013: A slightly different Z Head question....maybe
Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Robinson Salty Bottom, AL on Sunday, May 26, 2013 - 04:08 pm:

Today, I am installing a new Z Head (my 4th) and I feel that there may be a clearance problem between the piston and the head.

1. With the old head gasket removed, carbon removed from the pistons, head bolts snug- the crank will not spin because of contact.

2. With the old gasket installed for test purposes, the crank spins with zero contact.

3. With the old gasket installed for test purposes, .030 shims on top of the piston, the crank will spin, but contact is felt.

4. With the old gasket installed for test purposes, .024 shims on top of the piston, the crank will spin, no contact is felt, but Prussian Blue is transferred.

My question is: what is the minimum clearance acceptable between the piston and the head?

Z Head making contact


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, May 26, 2013 - 04:15 pm:

I think you need to have at least .050" clearance with the head torqued in place.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Memmelaar Jr on Sunday, May 26, 2013 - 04:52 pm:

I had the exact issue with mine when I installed it on my '12 touring car. I blues the tops of all the pistons and found that it was just slightly touching the head. a little dyna-file work and I was off to the races.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Robinson Salty Bottom, AL on Sunday, May 26, 2013 - 07:18 pm:

OK. This is what I did based upon Royce's .050 targeted clearance. Since nobody disagreed with him I am assuming that is a pretty safe clearance.

*I measured the thickness of the old head gasket (white fiberous center type) to be .041.

*I measured the new black centered type head gasket to be .070.

*That should give me .029 extra clearance. A total of .059.

* There should be .009 to spare, less any compression of the gasket. (a discarded black-cored head gasket from a previous install measures .063 after 3 years of running).

*Finally, round washers measuring .052 were blued, placed on top of the pistons as before, installed with the new gasket, and torqued to 40 ft lbs. Upon dia-assembly no blue was transferred.

Tomorrow, provided there is no fault found with my numbers or reasoning the final torque will be applied and the pickup will be on the road for a test drive.

Thank for the comments.


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